AR-15 in 300 Blackout advice.....

[saz]

Gentlemen,
I know the subject has been done to death, but here goes. I am new to building an AR-15, but I am not new to the weapon itself. Having been in the Army for 18 years, I have a little bit of experience with a M-4 bing deployed 5 times. Now I am looking to build a 300 Blackout as it would be more cast friendly at the velocities being used, and I can still hunt with it. What I have so far is a complete lower with 2 stage trigger, 16" bull barrel, and that is about it. Need the rest of the parts to finish the upper.

What I am looking for are pet loads preferable super-sonic, and what boolit feeds well. It has M-4 feed ramps, but I don't know if that would be a determining factor. Also most of the brass I have already is mil-surp, any issues with that? Again, I am very new to the cartridge and looking for advice/experience. Thanks everyone!

[Moonie]

My favorite load is the Lee .312-155gr boolit with 15.3gr of H110/W296. This feeds perfectly and gives me just over 1,800fps. The LC brass is generally considered the best to cut down for the 300BO.

[saz]

Does the 300 have any unreliable cycling with less than top end loads? I have heard of 5.56 not completely cycling with lighter loads. What would be considered "light"?

[garym1a2]

Same boolit with 15.0 grs of IMR4227 works for me, about 1720fps out of a 16 inch AR.

My favorite load is the Lee .312-155gr boolit with 15.3gr of H110/W296. This feeds perfectly and gives me just over 1,800fps. The LC brass is generally considered the best to cut down for the 300BO.

[Jailer]

Does the 300 have any unreliable cycling with less than top end loads? I have heard of 5.56 not completely cycling with lighter loads. What would be considered "light"?

If you go much less than that yes you will have cycling problems. Lilgun is about as fast a powder you can get away with using with a carbine gas system and still maintain reliable cycling with supers.

Ligun on the fast end and 4198 on the slow end for reliability with the AR platform.

Now get you a bolt gun in this caliber and you can really have some fun with it.

[ipijohn]

I am pushing the 312-155 Lee (powder coated) with 17.0 grn of A1680 with good accuracy (2 MOA) at about 1950 FPS . This load cycles my carbine length 16" AR and locks back on an empty mag.

[DrtRacr09]

I have been thinking if I build another about drilling out gas port to .125", maybe a hair bigger, and using an adjustable gas block. My barrel only had a .86 port and wouldn't function a case full of 296 with 110 V-Maxes, ended up at .110" port and perfect function at a lesser charge. Soon as I unbullet my brass it's Boolit's only.

[bugs1961]

Has anyone tried using a reduced power recoil spring to help with cycling reduced loads?

[saz]

Or how about a lightweight bolt?

[ipijohn]

Has anyone tried using a reduced power recoil spring to help with cycling reduced loads?

The first thing I did when trying to get my 5.56 AR to shoot lead boolits was to put a reduced power recoil spring in it. I have never taken it out and I shoot reduced 300 BLK loads with the same lower.

[Gunnut 45/454]

My all around load is the Lee 155 gr and 16 gr Lil'Gun runs around 1950 ish fps! Use 16.5 gr and you'll be pushing 2000 plus fps! Used the Lee 150 gr and 170 gr RN bullets as well mostly with W296 pretty hard on brass. I would love it if someone made a 130 gr mold that was reasonablely priced!

[bugs1961]

The first thing I did when trying to get my 5.56 AR to shoot lead boolits was to put a reduced power recoil spring in it. I have never taken it out and I shoot reduced 300 BLK loads with the same lower.

Excellent! Thanks.

[saz]

My all around load is the Lee 155 gr and 16 gr Lil'Gun runs around 1950 ish fps! Use 16.5 gr and you'll be pushing 2000 plus fps! Used the Lee 150 gr and 170 gr RN bullets as well mostly with W296 pretty hard on brass. I would love it if someone made a 130 gr mold that was reasonablely priced!

That is really good to know! I LOVE Lil'Gun! It got a bad rap when it was first introduced for being too "hot" but not an issue anymore.

Just to clarify, which Lee boolit are you talking about? I have heard many people talk about the Lee 155, but there are only these two molds- C309-150-F and C309-160-R. They look to be close to the same nose length, only one is a flatnose and one is round........

[wlc]

IIRC they are talking about the Lee .312-155. It will size down for use in the BLK.

[Jailer]

The Lee C309-160-R has to be seated way to deep in the case to make it a practical choice.

[Boolseye]

SAz,
I use the Lee 312-160 2R, OAL of 1.985" and 16 grains of RL 7 or 15.4 grains of 296. It's not real picky–so far it will feed every .30 cal boolit that I cast (C309-170, 309-230-5R, C312-185RN) I just bought a NOE 314299 that I will try, too.
Accurate, too, with everything. Sometimes you'll get a case with too much brass in the area of the new neck, after forming. If the thickness is over .014", it probably won't chamber. It's only one every 100 or so. Also, the heavies won't cycle the carbine gas system as easily.
-BE

[typz2slo]

Are you gas checking the boolits at these veloities?

[27judge]

RCBS 168gr sil with gas check 16.5-17.0 1680 one hole groups at 25 yards under 1 inch at 50 yards AR15 16.5 barrel. My grandkids and I burn this load up on the plinking range tks KEN

[HURK]

Where did you get the reduced power spring at? Midway? seems like the cast loads I made are stove piping. I used 1680 , with 10.7 grns , bullet is LEE 230 grns

[ipijohn]

Where did you get the reduced power spring at? Midway? seems like the cast loads I made are stove piping. I used 1680 , with 10.7 grns , bullet is LEE 230 grns

I think I got mine at Natchez